Conventionally, after an IC package is finished, it is delivered a downstream manufacturer to mount on a circuit board. During the delivery process, the silver epoxy between the chip and chip paddle is liable to separate (or delaminate) from the chip due to the thermal stress between the chip and chip paddle caused by the temperature variation. The delamination of the silver epoxy creates a gap where moisture tends to accumulate. Moreover, to mount the packaged IC on the circuit board, the IC is subjected to a high temperature solder reflow process. The high temperature process will evaporate the above-mentioned moisture in the delamination region, therefore, the undesirable pop-corning and cracking is occurred.
FIG. 1 and FIG. 2 shows the conventional package of IC. As shown in FIG. 1, The chip 13 is mounted on a chip paddle 11 with a smaller size. The chip 13 is adhered to the top of the chip paddle 11 by a silver epoxy 12. The bond pad of the chip 13 is electrically connected to the inner lead 15 of the leadframe through a bonding wire 14. The resultant structure is then encapsulated ay a plastic resin to form a complete packaged structure 10, as shown in FIG. 2. However, the above process has considered the attaching force between the chip and the paddle only, and is subjected to some problems. In one aspect, if the amount of the silver epoxy is deficient, the plastic resin is hard to fill up the space formed between the chip 13 and paddle 11, and beside the silver epoxy 12. Therefore, a gap or a void where the moisture is liable to accumulate is formed. The accumulated moisture will lead to the pop-corning and the cracking of the package during a high-temperature reflow process. In another aspect, if the amount of the silver epoxy is excessive, the silver epoxy 12 is apt to leak out of the adhesion region of the chip 13 and the paddle 11. The leakage of the silver epoxy 12 will contaminate the processing apparatus and then attach to the bottom surface of the paddle 11. The silver epoxy 12 on the bottom surface of the paddle 11 will deteriorate the binding force between the leadframe and the plastic resin due to the poor adhesive force between the silver epoxy 12 and the plastic resin. Therefore, a delamination problem is also occurred and the pop-corning of the package due to the evaporation of the accumulated moisture is hard to prevent.